I came accross a website where we can easily create ringtones by uploading
a file.
Cellsea is a web based Ringtone maker. Using their cool service you can
quickly create ringtones for yourself by uploading your audio files
(MP3, MIDI, M4A and AAC are supported). If your lazy to upload, they will
get the audio file for your from a remote URL or even a Google Search.

After uploading, you can crop your audio files and listen to preview
before sending it to production. The ringtone will be saved to Dashboard,
you can either download it to your machine and then upload it to your
cellphone over Bluetooth, Data Cable or IR. An simpler alternative would
be point your browser to wap.cellsea.com and then entering your download
code.

Note: The maximum upload size for audio files is just 5 MB, since
most MP3s thesedays are under 5 MB, this shouldn’t be an issue.